Many business and manufacturing operations require that a large number of objects be moved at a high rate of speed, where each individual object is moved in sequence as part of a continuous series of similar objects. Such operations frequently require that the weight of each individual object be measured before the object reaches a predetermined location. Examples of such operations would include packaging pharmaceutical capsules to determine whether or not each package contains a predetermined number of capsules; packaging electronic components to determine whether or not a package contains, for example, a predetermined number of transistors; packaging envelopes containing granular material; and mail sorting operations to determine the proper postage on each parcel.
The requirement for measuring the weight of each object may stem from the need to assure that each object contains a predetermined quantity of material. In that case, the measured weight information may be used to classify and physically sort the objects into groups, where each group of objects is classified according to predetermined weight values.
Other operations, however, may require that each item be labelled according to its own individual weight value. Information recorded on the label may simply indicate the gross weight of the object. In other cases, label information may be expressed in units which are proportional to weight as, for example, price of the object or the piece count of items contained in the object.
Automatic and high speed weighing of individual objects in a moving series of objects have been accomplished by a number of methods which are old and common in the art. But significant errors in the weight measurement often result from undesirable forces being introduced into the weight sensing function from sources other than weight of the object. Such erroneous forces may be caused by friction or vibration in the drive mechanism that moves the object. Other undesirable forces may result from aerodynamic effects on a rapidly moving object which has a large surface area relative to its mass.